1. Field of the Invention
The present invention relates to an electrophoretic display device and a manufacturing method thereof, and more particularly, to an electrophoretic display device for improving a reaction rate by forming a high-k dielectric layer using a high-k dielectric material in a conventional electrophoretic display device.
The present invention has been produced from the work supported by the IT R&D program of MIC (Ministry of Information and Communication)/IITA (Institute for Information Technology Advancement) [2005-S070-02, Flexible Display] in Korea.
2. Discussion of Related Art
Development of E-paper, one type of display device, began in the mid-1990s and research continues today in laboratories all over the world. E-paper has numerous applications, such as electronic newspaper, mobile compact displays, attachable displays, and displays for advertising. Electronic newspaper and electronic books are seen as being among the most promising applications, and it is anticipated that flexible electronic newspaper and a household electronic frame may be subject to priority development.
E-paper may be implemented using electrophoresis, the movement of charged particles in an applied electric field. When electrophoresis occurs in a fluid containing charged particles, the charged particles move with a velocity determined largely by their charge, viscous drag, the dielectric properties of the fluid, and the magnitude of the applied electric field.
An electrophoretic display device is bistable, and thus its color state persists even after an applied electric field is removed. The first electrophoretic reflective display device having this advantage was developed by Ota in the early 1970's (I. Ota, J. Ohnishi, and M. Yoshiyama, Proc. IEEE 61, p. 832, 1973), and research into such devices has been widespread ever since.
E-paper, one type of conventional electrophoretic display device, will be described below with reference to the accompanying drawings.
FIG. 1 schematically illustrates e-paper using two types of particles, and FIG. 2 schematically illustrates e-paper using one type of particles.
Referring to FIG. 1, conventional electrophoretic e-paper 10 includes first and second substrates 11 and 12 spaced from each other by a predetermined distance, and a plurality of capsules 13 formed between the first and second substrates 11 and 12. An electrode is formed on each of the first and second substrates 11 and 12, and while an electrode formed on the first substrate 11 is not shown in FIG. 1, an electrode 17 is formed on the second substrate 12 to correspond to each capsule 13. The capsules 13 include a fluid, i.e., a dielectric fluid 16 that fills the inside of the capsule 13, and first and second particles 14 and 15 that are suspended in the dielectric fluid 16 and have different colors from the fluid. Here, the first particles 14 are titanium oxide particles, and the second particles 15 are colored particles.
Referring to FIG. 2, e-paper 20 includes first and second substrates 11 and 12, and a plurality of capsules 13 formed therebetween, like the e-paper 10 illustrated in FIG. 1. The capsules 13 illustrated in FIG. 2 include a colorant solution 16a as the dielectric fluid, and first particles 14 formed of titanium oxide. Other components are the same as in FIG. 1, and thus a detailed description thereof will be omitted.
The electrophoretic e-paper shown in FIG. 1 has a structure in which two types of particles having different colors and the dielectric fluid are included in the capsules 13, and the electrophoretic e-paper shown in FIG. 2 has a structure in which one type of particles and a colorant solution are included in the capsules 13. In both cases, the color of the paper is determined by the particles included in the capsules 13. When an electric field is applied to particles having one or more colors, oppositely charged particles move towards oppositely charged electrodes, causing a visually observable change in color.
However, when electrophoretic e-paper is manufactured, the densities of the charged particles and the dielectric fluid are made the same to prevent the charged particles from settling on the bottom. However, clustering and agglomeration of particles occurs over time due to dispersion instability and eventually leads to particle instability. This poses an obstacle to commercialization (refer to P. Murau and B. Singer, J. Appl. Phys., vol. 49, p. 4820, 1978).
In addition, lowering an operating voltage in order to reduce power consumption of the electrophoretic e-paper may excessively weaken the electric field across the capsules because the e-paper structurally includes interfaces and other elements between the capsules, a binder, and the electrodes.